Is it ok to use ReactDOMServer.renderToString in the browser in areas where React isn't directly managing the DOM?

According to the new documentation: https://reactjs.org/docs/react-dom-server.html

The following methods can be used in both the server and browser environments:

• renderToString()
• renderToStaticMarkup()

I know it is too old question, but since it has not been answered I wanted to share my thoughts.

I was using the same thing, renderToString, but as the documentation recommends not to use it on client-side, I achieved it in another way, by using the react-dom's render method to render the custom component into div

var myDiv = document.createElement('div');

ReactDOM.render(
  <MarkerContents data={this.props.data} />,
  myDiv
);

var myIcon = L.divIcon({ 
    iconSize: new L.Point(50, 50), 
    html: myDiv.innerHTML
});

As Thomas already said, yes, you can use renderToString on the client. Just to be clear though, you will need to import ReactDOMServer on the client, which may seem counter-intuitive but appears to be correct. Example (on the client):

import React from 'react';
import ReactDOMServer from 'react-dom/server';

const MyComp = (props) => {
  const html = ReactDOMServer.renderToString(<div>{someFunc(props)}</div>);
  // do something with your html, then
  return <div dangerouslySetInnerHTML={{__html: html}}></div>;
};